1. Field of the Invention
This invention relates to the production of sodium carbonate from a complex brine such as that which occurs naturally at Searles Lake, California or from an artificial brine by carbonating the brine to form sodium bicarbonate, crystallizing the sodium bicarbonate and drying the crystallized sodium bicarbonate to form sodium carbonate, and recystallizing the sodium carbonate to form a dense ash, finished product.
2. Description of the Prior Art
Various methods have been disclosed in the past for the production of sodium carbonate and sodium bicarbonate from complex brines such as naturally occur at Searles Lake, California or from artificial brines containing sodium carbonate and, or, sodium hydroxide. Examples of these processes are provided by U.S. Pat. Nos. 1,000,138 and 1,016,239 issued to Wrinkle et al, U.S. Pat. No. 1,215,543 issued to Jones et al, U.S. Pat. No. 1,330,573 issued to Bacon et al, U.S. Pat. No. 1,674,474 issued to Kuhnert, U.S. Pat. No. 1,865,833 issued to Chesny and U.S. Pat. No. 2,784,056 issued to Wiseman.
Basically, these processes provided for the carbonation of the brine to provide a saturated solution from which sodium bicarbonate was separated from the brine and it was customarily calcined to produce sodium carbonate.
All of the above processes have experienced some success but problems have still been present. Normally, in drying material such as bicarbonates wherein there are filtration and drying processes it has been found that a maximum permissible feed "free moisture" content exists from the filtration process to enable the bicarbonate to be adequately dried. In many instances, the free moisture content after filtration has been found to exceed 20 percent by weight of the feed.
The basic problem caused by such excessive free moisture has been a tendency for the feed material to stick to the heat transfer surfaces of the dryer as the feed enters the drying unit, thus fouling and or plugging of the dryer results and process shutdown is required. This problem has been remedied in the past by mixing with the moisture laden feed a recycle stream of dried sodium carbonate to reduce the moisture content of the feed to a point below which the sticking tendency is no longer prevalent. This has previously resulted in recycle ratios in excess of 3 to 1 for the dried sodium carbonate to moisture laden feed and as a result the size of the dryer vessel has been determined by the necessary capacity required to handle the combined feed and recycle rather than the heat transfer capability of the dryer vessel. Thus, larger, considerably more expensive dryers were required to be used to successfully dry the bicarbonate than would otherwise be necessary.
An additional problem which has arisen with the advent of environmental pollution standards and the increased costs of producing carbon dioxide for process uses has been the removal of non-condensable gases from the steam tubes utilized to heat the dryer vessels. In the past, such heating systems have been designed such that the steam tubes penetrated the end of the dryer from which the feed enters and were collected in a manifold system for removal.
Normally, the point at which the steam tubes penetrated the dryer endwall was provided with a flexible packing seal to allow for expansion of the steam tubes but prevent process off gases, primarily carbon dioxide, and dust produced in the dryer vessel from escaping into the atmosphere during some operating conditions while also preventing air inleakage and consequent dilution of the carbon dioxide containing off gas produced therein at other operating conditions. The various seals which have been developed have each necessitated frequent maintenance and replacements, necessitating process shut-downs leading to less economical processes than would otherwise be possible if this problem could be eliminated.
Thus far, in spite of the drawbacks described above in the production of sodium carbonate from sodium bicarbonate recovered from naturally occurring or artificial brines, no process has been developed to satisfactorily alleviate these problems.